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Heat transfer fluids are used as a low-cost way to heat process equipment, such as in plastics molding. Selecting a heat transfer fluid depends on the system operating temperature range. Fluids should not be used below the fluid’s pumpability point, which is the temperature where fluid becomes too thick to flow. The recommended maximum bulk fluid operating temperature is the highest temperature at which the fluid will withstand thermal cracking or thermal degradation. Petroleum-based and synthetic-based heat transfer fluids have a wide temperature range that largely overlaps, but synthetic-based heat transfer fluids are recommended for higher operating temperatures.

Thermal degradation occurs when heat transfer fluid is heated past its maximum bulk fluid operating temperature, or boiling point. Thermal degradation commonly causes four types of degradation products known as ‘low boilers’, ‘high boilers’, gaseous decomposition products, and sludge. These are defined by the boiling range distribution determined using a gas chromatograph to perform a simulated distillation on a fluid that has been exposed to thermal stress.

Low boilers are defined as the liquid components of a stressed fluid that boil at a temperature below the initial boiling point of an unstressed sample of the same fluid. These are caused when the carbon-carbon bonds in the fluid molecules are cracked by high temperatures; when the reaction stops at this point, smaller molecules than originally existed are formed. Low boilers are evident in heat transfer fluid when the flash point and viscosity of the fluid decrease and the vapor pressure increases. A higher vapor pressure can affect system efficiency and lead to premature failure of certain parts. A lower flash point can also be a safety and operating concern.

High boilers are defined as liquid components of a stressed fluid that boil at a temperature above the final boiling point of an unstressed sample of the same fluid. These are caused when the carbon-carbon bonds are cracked by extremely high temperatures; the molecules then react with each other to form larger polymeric molecules. High boilers cause higher viscosity, but can eventually lead to coke fouling on the heat transfer surfaces. When thermal degradation reaches this point, the fouling is rapid and the system soon ceases to operate.

We can perform a wide range of tests on heat transfer fluids, including some highly specialized tests. We can perform ASTM D6743, thermal stability of heat transfer fluids, at temperatures exceeding 450c. We can also test viscosity and density at temperature up to 350c and true vapor pressure at temperatures up to 380c.

Our Alcor hot liquid process simulator (Alcor HLPS) instrument can also be used to simulate an entire heat transfer system. This is particularly useful in R&D to test fluid performance under extreme temperature and pressure conditions and in application engineering to identify which fluid can be expected to perform better under extreme operating conditions. This test is more similar to real-world conditions than pure thermal stress from ASTM D6743.

Below is a list of the most common heat transfer fluid-related tests that we perform. If you are interested in testing a sample according to a specification or method that is not listed below, please contact us so that we can work with you to customize our testing to your needs. To learn more about a test, click on the test method number.